SIM full form: Subscriber Identity Module

How to say it: as a word, not letter by letter.

SIM stands for Subscriber Identity Module. It is the small chip card, or the chip built into a phone, that tells the mobile network who you are, so that calls, messages and data are connected to your number and your account.

What is on a SIM

The SIM stores a unique identity number for your connection and a secret key that the network uses to check that the SIM is genuine. Your phone number is tied to that identity in the operator's records, which is why the number moves with the SIM when you put it in another phone.

Sizes, and the eSIM

• Mini SIM, the old standard size.
• Micro SIM, smaller.
• Nano SIM, the size most phones use now.
• eSIM, the embedded SIM: a chip fixed inside the phone, set up by scanning a QR code from the operator.

Numbers connected with a SIM

• ICCID: Integrated Circuit Card Identifier, the long serial number printed on the card.
• IMSI: International Mobile Subscriber Identity, the number that identifies the subscriber to the network.
• IMEI: International Mobile Equipment Identity. This belongs to the handset, not the SIM.
• PUK: PIN Unblocking Key, needed if a SIM PIN is entered wrongly too many times.
• MNP: Mobile Number Portability, keeping your number when changing operator.

SIM swap fraud

Because OTPs come to your number, a criminal who gets a duplicate SIM in your name can receive them. If your phone suddenly shows no network for a long time for no reason, contact your operator and your bank quickly. Never share SIM details, or codes sent by the operator, with a caller.

More mobile and telecom full forms

• CDMA Code Division Multiple Access
• LTE Long Term Evolution
• VoLTE Voice over LTE
• 5G Fifth Generation
• IMEI International Mobile Equipment Identity
• GPS Global Positioning System
• NavIC Navigation with Indian Constellation
• STD Subscriber Trunk Dialling

All mobile and telecom Next: GPS explained

Check what matters. These pages explain names and terms in general. Rules, dates, fees and limits change: take them from the official body. Read on 12 November 2026.